1. Field of the Invention
The present invention is related to surface temperature measurement where visual access is readily available and, more particularly, to a method and apparatus for quantitative surface temperature measurement of a model in a hypersonic wind tunnel.
2. Description of the Related Art
Evaluation of designs for vehicles traveling at high speeds, particularly vehicles launched into space from earth or returning to earth from space, requires aerothermodynamic data regarding the effects of high speed air flow around the vehicle. This data is typically obtained by testing models in hypersonic wind tunnels capable of generating air speeds up to Mach 10. The measurement of primary interest is heat transfer rate to the model surface. Conventionally, these measurements are obtained by either discrete measurement of the surface temperature - time history, using thermocouples or thin-film resistance gauges, or thermal mapping via optical techniques such as photographing phase change paint, color sensitive paint, liquid crystal patterns, infrared sensitive measuring devices or thermographic phosphors. Each technique has its own advantages and disadvantages. The discrete measurement techniques provide detailed quantitative information, but models for wind tunnel tests are expensive to produce and the temperature information obtained is only at selected spots, not the entire surface of the model. The thermal mapping techniques can be used with less expensive models, but the temperature information obtained is essentially qualitative, making comparison between different models difficult.